How is interaction between different layers and components organized in a multi-layer system architecture?

In a multi-layered system architecture, interaction between layers and components usually occurs through well-defined interfaces and protocols. For example, in iOS, the MVC or MVVM pattern is often used, where the View interacts with the ViewModel or Controller, which in turn access the data model. Communication can be carried out via delegates, notifications (NotificationCenter), closures, or reactive libraries (Combine, RxSwift).

Example of interaction via delegate:

protocol DataUpdateDelegate: AnyObject {
    func didUpdateData(_ data: String)
}

class Model {
    weak var delegate: DataUpdateDelegate?
    func fetchData() {
        // Fetching data
        let data = "New data"
        delegate?.didUpdateData(data)
    }
}

class ViewController: UIViewController, DataUpdateDelegate {
    let model = Model()
    override func viewDidLoad() {
        super.viewDidLoad()
        model.delegate = self
        model.fetchData()
    }
    func didUpdateData(_ data: String) {
        print("Updated data: \(data)")
    }
}